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[109.157.47.110]) by smtp.gmail.com with ESMTPSA id o70sm12792801wme.29.2019.10.11.10.08.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 11 Oct 2019 10:08:48 -0700 (PDT) Subject: Re: [PATCH 01/11] graph: automatically track visible width of `strbuf` To: Johannes Schindelin , James Coglan via GitGitGadget Cc: git@vger.kernel.org, Junio C Hamano References: <4bc0a0596164212aa9d29d6dd0d7a0d8ab1b9dd0.1570724021.git.gitgitgadget@gmail.com> From: James Coglan Message-ID: <16547350-2997-d250-d48b-43c6ae49b3c3@gmail.com> Date: Fri, 11 Oct 2019 18:08:47 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Hi Johannes, On 10/10/2019 22:07, Johannes Schindelin wrote: > Hi James, > > On Thu, 10 Oct 2019, James Coglan via GitGitGadget wrote: > >> From: James Coglan >> >> All the output functions in `graph.c` currently keep track of how many >> printable chars they've written to the buffer, before calling >> `graph_pad_horizontally()` to pad the line with spaces. Some functions >> do this by incrementing a counter whenever they write to the buffer, and >> others do it by encoding an assumption about how many chars are written, >> as in: >> >> graph_pad_horizontally(graph, sb, graph->num_columns * 2); >> >> This adds a fair amount of noise to the functions' logic and is easily >> broken if one forgets to increment the right counter or update the >> calculations used for padding. >> >> To make this easier to use, I'm adding a `width` field to `strbuf` that >> tracks the number of printing characters added after the line prefix. > > This is a big heavy-handed: adding a `width` field to `struct strbuf` > and maintaining it _just_ for the purpose of `graph.c` puts an > unnecssary load on every other `strbuf` user (of which there are a > _lot_). I was anticipating there might be objections to modifying a widely used struct. There are other idea I had for solving this that I can share -- I'll post an alternative to this patch shortly that does not involve changing `strbuf`. > So my obvious question is: what makes `width` different from `len`? > Since we exclusively use ASCII characters for the graph part, we should > be able to use the already-existing `len`, for free, no? `len` counts the number of bytes in the buffer, which may include non-printing bytes used to apply color formatting. For padding graph lines, we need to know the number of display columns the buffer will use, and that's what `width` was added for. > I could imagine that the `strbuf` might receive more than one line, but > then we still would only need to remember the offset of the last newline > character in that `strbuf`, no? As far as I know, it does not contain multiple lines when used in graph.c, but I agree the implementation I've submitted here is obviously wrong if you wanted to use it to get the width of multi-line text. Putting code in strbuf that only works in graph.c and not more broadly was probably a mistake on my part. > >> It's set to 0 at the start of `graph_next_line()`, and then various >> `strbuf` functions update it as follows: >> >> - `strbuf_write_column()` increments `width` by 1 >> >> - `strbuf_setlen()` changes `width` by the amount added to `len` if >> `len` is increased, or makes `width` and `len` the same if it's >> decreased >> >> - `strbuf_addch()` increments `width` by 1 >> >> This is enough to ensure that the functions used by `graph.c` update >> `strbuf->width` correctly, and `graph_pad_horizontally()` can then use >> this field instead of taking `chars_written` as a parameter. >> >> Signed-off-by: James Coglan >> --- >> graph.c | 68 ++++++++++++++++++++++---------------------------------- >> strbuf.h | 8 ++++++- >> 2 files changed, 33 insertions(+), 43 deletions(-) >> >> diff --git a/graph.c b/graph.c >> index f53135485f..c56fdec1fc 100644 >> --- a/graph.c >> +++ b/graph.c >> @@ -115,11 +115,20 @@ static const char *column_get_color_code(unsigned short color) >> static void strbuf_write_column(struct strbuf *sb, const struct column *c, >> char col_char) >> { >> + /* >> + * Remember the buffer's width as we're about to add non-printing >> + * content to it, and we want to avoid counting the byte length >> + * of this content towards the buffer's visible width >> + */ >> + size_t prev_width = sb->width; >> + >> if (c->color < column_colors_max) >> strbuf_addstr(sb, column_get_color_code(c->color)); >> strbuf_addch(sb, col_char); >> if (c->color < column_colors_max) >> strbuf_addstr(sb, column_get_color_code(column_colors_max)); >> + >> + sb->width = prev_width + 1; >> } >> >> struct git_graph { >> @@ -686,8 +695,7 @@ static int graph_is_mapping_correct(struct git_graph *graph) >> return 1; >> } >> >> -static void graph_pad_horizontally(struct git_graph *graph, struct strbuf *sb, >> - int chars_written) >> +static void graph_pad_horizontally(struct git_graph *graph, struct strbuf *sb) >> { >> /* >> * Add additional spaces to the end of the strbuf, so that all >> @@ -696,8 +704,8 @@ static void graph_pad_horizontally(struct git_graph *graph, struct strbuf *sb, >> * This way, fields printed to the right of the graph will remain >> * aligned for the entire commit. >> */ >> - if (chars_written < graph->width) >> - strbuf_addchars(sb, ' ', graph->width - chars_written); >> + if (sb->width < graph->width) >> + strbuf_addchars(sb, ' ', graph->width - sb->width); >> } >> >> static void graph_output_padding_line(struct git_graph *graph, >> @@ -723,7 +731,7 @@ static void graph_output_padding_line(struct git_graph *graph, >> strbuf_addch(sb, ' '); >> } >> >> - graph_pad_horizontally(graph, sb, graph->num_new_columns * 2); >> + graph_pad_horizontally(graph, sb); >> } >> >> >> @@ -740,7 +748,7 @@ static void graph_output_skip_line(struct git_graph *graph, struct strbuf *sb) >> * of the graph is missing. >> */ >> strbuf_addstr(sb, "..."); >> - graph_pad_horizontally(graph, sb, 3); >> + graph_pad_horizontally(graph, sb); >> >> if (graph->num_parents >= 3 && >> graph->commit_index < (graph->num_columns - 1)) >> @@ -754,7 +762,6 @@ static void graph_output_pre_commit_line(struct git_graph *graph, >> { >> int num_expansion_rows; >> int i, seen_this; >> - int chars_written; >> >> /* >> * This function formats a row that increases the space around a commit >> @@ -777,14 +784,12 @@ static void graph_output_pre_commit_line(struct git_graph *graph, >> * Output the row >> */ >> seen_this = 0; >> - chars_written = 0; >> for (i = 0; i < graph->num_columns; i++) { >> struct column *col = &graph->columns[i]; >> if (col->commit == graph->commit) { >> seen_this = 1; >> strbuf_write_column(sb, col, '|'); >> strbuf_addchars(sb, ' ', graph->expansion_row); >> - chars_written += 1 + graph->expansion_row; >> } else if (seen_this && (graph->expansion_row == 0)) { >> /* >> * This is the first line of the pre-commit output. >> @@ -800,19 +805,15 @@ static void graph_output_pre_commit_line(struct git_graph *graph, >> strbuf_write_column(sb, col, '\\'); >> else >> strbuf_write_column(sb, col, '|'); >> - chars_written++; >> } else if (seen_this && (graph->expansion_row > 0)) { >> strbuf_write_column(sb, col, '\\'); >> - chars_written++; >> } else { >> strbuf_write_column(sb, col, '|'); >> - chars_written++; >> } >> strbuf_addch(sb, ' '); >> - chars_written++; >> } >> >> - graph_pad_horizontally(graph, sb, chars_written); >> + graph_pad_horizontally(graph, sb); >> >> /* >> * Increment graph->expansion_row, >> @@ -842,11 +843,9 @@ static void graph_output_commit_char(struct git_graph *graph, struct strbuf *sb) >> } >> >> /* >> - * Draw the horizontal dashes of an octopus merge and return the number of >> - * characters written. >> + * Draw the horizontal dashes of an octopus merge. >> */ >> -static int graph_draw_octopus_merge(struct git_graph *graph, >> - struct strbuf *sb) >> +static void graph_draw_octopus_merge(struct git_graph *graph, struct strbuf *sb) >> { >> /* >> * Here dashless_parents represents the number of parents which don't >> @@ -890,13 +889,12 @@ static int graph_draw_octopus_merge(struct git_graph *graph, >> strbuf_write_column(sb, &graph->new_columns[i+first_col], >> i == dashful_parents-1 ? '.' : '-'); >> } >> - return 2 * dashful_parents; >> } >> >> static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb) >> { >> int seen_this = 0; >> - int i, chars_written; >> + int i; >> >> /* >> * Output the row containing this commit >> @@ -906,7 +904,6 @@ static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb) >> * children that we have already processed.) >> */ >> seen_this = 0; >> - chars_written = 0; >> for (i = 0; i <= graph->num_columns; i++) { >> struct column *col = &graph->columns[i]; >> struct commit *col_commit; >> @@ -921,14 +918,11 @@ static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb) >> if (col_commit == graph->commit) { >> seen_this = 1; >> graph_output_commit_char(graph, sb); >> - chars_written++; >> >> if (graph->num_parents > 2) >> - chars_written += graph_draw_octopus_merge(graph, >> - sb); >> + graph_draw_octopus_merge(graph, sb); >> } else if (seen_this && (graph->num_parents > 2)) { >> strbuf_write_column(sb, col, '\\'); >> - chars_written++; >> } else if (seen_this && (graph->num_parents == 2)) { >> /* >> * This is a 2-way merge commit. >> @@ -948,16 +942,13 @@ static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb) >> strbuf_write_column(sb, col, '\\'); >> else >> strbuf_write_column(sb, col, '|'); >> - chars_written++; >> } else { >> strbuf_write_column(sb, col, '|'); >> - chars_written++; >> } >> strbuf_addch(sb, ' '); >> - chars_written++; >> } >> >> - graph_pad_horizontally(graph, sb, chars_written); >> + graph_pad_horizontally(graph, sb); >> >> /* >> * Update graph->state >> @@ -984,12 +975,11 @@ static struct column *find_new_column_by_commit(struct git_graph *graph, >> static void graph_output_post_merge_line(struct git_graph *graph, struct strbuf *sb) >> { >> int seen_this = 0; >> - int i, j, chars_written; >> + int i, j; >> >> /* >> * Output the post-merge row >> */ >> - chars_written = 0; >> for (i = 0; i <= graph->num_columns; i++) { >> struct column *col = &graph->columns[i]; >> struct commit *col_commit; >> @@ -1017,7 +1007,6 @@ static void graph_output_post_merge_line(struct git_graph *graph, struct strbuf >> assert(par_column); >> >> strbuf_write_column(sb, par_column, '|'); >> - chars_written++; >> for (j = 0; j < graph->num_parents - 1; j++) { >> parents = next_interesting_parent(graph, parents); >> assert(parents); >> @@ -1026,19 +1015,16 @@ static void graph_output_post_merge_line(struct git_graph *graph, struct strbuf >> strbuf_write_column(sb, par_column, '\\'); >> strbuf_addch(sb, ' '); >> } >> - chars_written += j * 2; >> } else if (seen_this) { >> strbuf_write_column(sb, col, '\\'); >> strbuf_addch(sb, ' '); >> - chars_written += 2; >> } else { >> strbuf_write_column(sb, col, '|'); >> strbuf_addch(sb, ' '); >> - chars_written += 2; >> } >> } >> >> - graph_pad_horizontally(graph, sb, chars_written); >> + graph_pad_horizontally(graph, sb); >> >> /* >> * Update graph->state >> @@ -1181,7 +1167,7 @@ static void graph_output_collapsing_line(struct git_graph *graph, struct strbuf >> } >> } >> >> - graph_pad_horizontally(graph, sb, graph->mapping_size); >> + graph_pad_horizontally(graph, sb); >> >> /* >> * Swap mapping and new_mapping >> @@ -1199,6 +1185,8 @@ static void graph_output_collapsing_line(struct git_graph *graph, struct strbuf >> >> int graph_next_line(struct git_graph *graph, struct strbuf *sb) >> { >> + sb->width = 0; >> + >> switch (graph->state) { >> case GRAPH_PADDING: >> graph_output_padding_line(graph, sb); >> @@ -1227,7 +1215,6 @@ int graph_next_line(struct git_graph *graph, struct strbuf *sb) >> static void graph_padding_line(struct git_graph *graph, struct strbuf *sb) >> { >> int i; >> - int chars_written = 0; >> >> if (graph->state != GRAPH_COMMIT) { >> graph_next_line(graph, sb); >> @@ -1245,19 +1232,16 @@ static void graph_padding_line(struct git_graph *graph, struct strbuf *sb) >> struct column *col = &graph->columns[i]; >> >> strbuf_write_column(sb, col, '|'); >> - chars_written++; >> >> if (col->commit == graph->commit && graph->num_parents > 2) { >> int len = (graph->num_parents - 2) * 2; >> strbuf_addchars(sb, ' ', len); >> - chars_written += len; >> } else { >> strbuf_addch(sb, ' '); >> - chars_written++; >> } >> } >> >> - graph_pad_horizontally(graph, sb, chars_written); >> + graph_pad_horizontally(graph, sb); >> >> /* >> * Update graph->prev_state since we have output a padding line >> diff --git a/strbuf.h b/strbuf.h >> index f62278a0be..3a98147321 100644 >> --- a/strbuf.h >> +++ b/strbuf.h >> @@ -66,11 +66,12 @@ struct string_list; >> struct strbuf { >> size_t alloc; >> size_t len; >> + size_t width; >> char *buf; >> }; >> >> extern char strbuf_slopbuf[]; >> -#define STRBUF_INIT { .alloc = 0, .len = 0, .buf = strbuf_slopbuf } >> +#define STRBUF_INIT { .alloc = 0, .len = 0, .width = 0, .buf = strbuf_slopbuf } >> >> /* >> * Predeclare this here, since cache.h includes this file before it defines the >> @@ -161,6 +162,10 @@ static inline void strbuf_setlen(struct strbuf *sb, size_t len) >> { >> if (len > (sb->alloc ? sb->alloc - 1 : 0)) >> die("BUG: strbuf_setlen() beyond buffer"); >> + if (len > sb->len) >> + sb->width += len - sb->len; >> + else >> + sb->width = len; >> sb->len = len; >> if (sb->buf != strbuf_slopbuf) >> sb->buf[len] = '\0'; >> @@ -231,6 +236,7 @@ static inline void strbuf_addch(struct strbuf *sb, int c) >> strbuf_grow(sb, 1); >> sb->buf[sb->len++] = c; >> sb->buf[sb->len] = '\0'; >> + sb->width++; >> } >> >> /** >> -- >> gitgitgadget >> >>